With current perpendicular magnetic recording technology, the magnetic recording areal density has been pushed to around 500˜600 Gb/in2, and has almost reached the physical upper limit imposed by the superparamagnetic effect. Even with the availability of a higher coercivity magnetic material such as FePt and CoPd, a poor writability resulting from saturation of the writing head is expected to become a bottle neck. Energy Assisted Magnetic Recording (EAMR) or Heat Assisted Magnetic Recording (HAMR) technology has become the common pursuit in data storage circle, since the technology offers a way to circumvent the writability bottleneck and further push the data areal density to 1 Tbit/in2 and beyond. The EAMR/HAMR technology can eventually merge with the patterned media.
Near Field Transducer (NFT) is a critical element for an EAMR or HAMR head to transfer enough energy to a tiny bit region and heat the region up to a temperature close to the Currier Temperature temporarily so as to achieve the writability within the short duration. The scalability of the data areal density is determined by that of the NFT, and the writability of a recording layer with a very high coercivity material depends on the NFT delivery efficiency. All known NFT designs have a relatively low delivery efficiency, typically in the range of just a few percent.
FIG. 1 is a diagram depicting an exemplary optical module 100 in which light energy generated by a light source 110 (e.g., laser diode) is coupled to a waveguide 130 via a coupler 120. The coupler 120 can be a grating or simple butt coupling. Some of the light energy is lost in the coupler 120 due to scattering 101. The waveguide 130 guides and directs the light energy to a near field transducer (NFT) 140 and a recording media 150. While in the waveguide 130, some of the light energy is lost by scattering 103 in the waveguide due to process imperfections and also to the surrounding pole as pole absorption 104. The NFT 140 focuses the light energy received from the waveguide 130 into a nano-sized light beam and delivers the beam to the recording media so as to heat up a specific recording region thereof. Some of the light energy received by the NFT 106 is also lost due to NFT absorption 106. At least part of the light energy delivered to the recording media 150 from the NFT 140 is absorbed by the recording media as media absorption 105. Energy losses from the light source 110, the coupler scattering 101, and waveguide scattering 103 result in heat dissipation into slider 102.
As mentioned above, the NFT delivery efficiency is only a few percent, so power requirement for the light source 110 is quite high. For example, heat dissipation by a laser diode needs special care with consideration of the 30˜40% of lasering efficiency and the light absorption by the adjacent magnetic elements due to the interaction of scattering light from waveguide resultant from taper, bend and process imperfections. Furthermore, besides the portion of energy delivered to the media 150, the absorption by the NFT 140 itself together with the pole absorption 104 can heat up the NFT 140 to a very high temperature at which the NFT 140 may melt and lose its function. Therefore, an improved heat management by minimizing energy losses is highly desired. One optimal way of minimizing the power requirement for the light source 110 is to maximize energy absorption in the media 150, especially in a recording layer thereof.
In certain aspects, the present disclosure provides a media stack design that maximizes the utilization efficiency of the electromagnetic energy delivered to the media from the NFT.